Non-ridging stainless steels



United States Patent NON-RIDGING STAINLESS STEELS Charles T. Evans, Jr., Pittsburgh, Pa., assignor to Universal-Cyclops Steel Corporation, Bridgeville, Pa., a corporation of Pennsylvania No Drawing. Filed Jan. 26, 1959, Ser. No. 788,763

7 Claims. (Cl. 75-126) This invention relates to stainless steels that can be used for deep drawing operations without encountering the phenomenon known in the art as ridging, roping or washboard.

A major object of the present invention is to provide stainless steel alloys, and shapes thereof including strip, that are characterized by the capability of being drawn and formed to various shapes without encountering ridging or roping.

7 Stainless steels of the type exemplified by American Iron and Steel Institute classification Type 430 are widely used in the automotive industry for decorative applications. Generally, the steel is drawn to the desired shape and then polished to a high finish.

Where deep drawing is practiced, as in forming automobile wheel covers and in similar applications, the resulting product frequently exhibits a phenomenon called ridging or roping. This is exhibited as a plurality of directional lines or hands that appear on the surface. These lines are unsightly and must be removed. Polishing is effective for that purpose where only moderate ridging occurs, but it usually is diflicult and expensive.

In view of the seriousness of this problem and the difliculty and expense involved in overcoming it, there is no surprise in the fact that research eiforts have been exerted to relieve the situation. That research has resulted in several inventions directed to overcoming ridging. For example, the recent patent to Waxweiler, No. 2,851,384, shows one approach to the problem. Briefly stated, Waxweiler discovered that n'dging could be diminished in Type 430 stainless steels, and similar ferritic stainless steels, by controlling the austenite present at the normalizing temperature. That involves a special heat treatment schedule. Waxweiler further reports that attempts to control ridging by use of alloying additives proved a failure (col. 3, lines to 24).

Another approach to the control of ridging is shown in the patent to Leflingwell et al., No. 2,808,353. Here, too, the solution is said to be in the use of a particular rolling and heat treating schedule.

The present invention relates to controlling the same phenomenon described in the above-identified patents, but the approach is entirely different. It has now been discovered that ridging can be avoided in ferritic stainless steels by including in those compositions a small amount of columbium effective to avoid ridging or roping. The resulting products can be used in the same manner that the Type 430 and analogous stainless steels are now used, but with the advantage that roping and ridging is not encountered.

Steels to which the present discoveries apply are substantially straight chrome steels. There are now known to the art several steels that ordinarily form the base stock for various articles of a decorative nature used in connection with automobiles and similar applications. Those constitute the most important materials to which the present invention is to be applied in view of the experience fabricators and users have with these wellknown materials. The A. I. S. I. Type 430 and its variations are representative of the usual steels that are to be modified in accordance with the present invention.

The stainless ferritic steels embodying the present invention and by which its stated objects are attained contain, by weight, about 14 to 25 percent of chromium, up to a maximum of about 0.60 percent of carbon, up to about 1.25 percent of manganese, a maximum of one percent of silicon, about.0.01 to 1 percent of columbium and the remainder iron and incidental impurities. Where phosphorus and sulfur are present, they do not exceed about 0.04 and 0.03 percent respectively. In addition alloying constituents may be included to develop special characteristics as desired, provided they do not detract from the non-ridging characteristics of the resulting products.

Within the foregoing broad range, intermediate ranges are definitive of steels that are of particular interest, usually as a consequence of an intended application. A suitable intermediate range of ferritic stainless steel compositions in accordance with this invention includes, by weight, 14 to 18 percent of chromium, 0.20 percent maximum of carbon, a maximum of 1 percent of manganese, a maximum of 1 percent of silicon, a maximum of 0.04 percent of phosphorous, a maximum of 0.03 percent of sulfur, about 0.1 to 0.7 percent of columbium with the remainder iron except for incidental impurities and alloying constituents as above described. It will be noted that in the preferred range of compositions, the chromium and other constituents are present in quantities typifying Type 430 steel.

Columbium is used in the invention in small but effective amounts that generally do not exceed about one percent based on the total weight of the compositions. Different columbium contents may be used in different instances depending on the balance of the composition. Within the broad range it is preferred to use about 0.2 to 0.70, and more suitably 0.3 to 0.60 weight percent of columbium; It should be understood that the columbium used may be substantially pure or may contain a small amount of tantalum. For purposes of this invention the tantalum present, if any, is simply considered as columbium.

The invention will be described further in conjunction with the following example in which the details are given by way of illustration and not by way of limitation.

A 26,500 pound heat of Type 430 stainless steel was prepared by melting a low carbon iron along with chromium in a production furnace. The materials were chosen to provide a 0.5 to 0.6 weight percent manganese melting aim. About 0.45 weight percent of columbium was added to the melt. Ingots were poured from the heat and when solidified were cooled and were cold worked to strip and annealed in accordance with standard practices for Type 430 steel. The analysis of this heat follows:

TABLE Weight Percent C 0.078 Mn 0.50 Si 0.46 S 0.007 P 0.018 Cr 16.63 Cb (+Ta) 0.45

Strip of this material was deep drawn in the laboratory. Close visual inspection of the products failed to disclose any evidence of ridging. Additional quantities of this strip were supplied to an automobile wheel cover manufacturer to field test the invention. Experience has shown that the drawing of wheel covers is extremely severe and will demonstrate ridging if it will occur with the alloy in question. In this test and others made along the same general lines and in accordance with standard production conditions, it was found that no ridging occurred. This is considered particularly significant because wheel covers drawn in the same fashion with Type 430 steel made to the same melting aim, except omitting the columbium addition made in this invention, demonstrate considerable ridging.

From the foregoing it is evident that the present invention constitutes a unique advance in preventing ridging inferritic stainless steels. The invention marks a clear departure from the prior art which shows that heat treatment was considered to be the best manner of overcoming this phenomenon. The invention is particularly surprising in that, contrary to the express teachings found in prior art, it shows that ridging can be effectively controlled through use of an alloying addition. This discovery therefore permits standard production and utilization practices to be carried out and does not require use of special heat treating and rolling schedules.

In accordance with the provisions of the patent statutes, I have explained the principle of my invention and have described What I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1.A non-ridging ferritic stainless steel consisting essentially, .by weight, of about 14 to 25 percent of chromium, up to about 0.60 percent of carbon, up to abount 1.25 percent of manganese, a maximum of one percent of silicon, a small amount that is less than one percent of columbium effective to characterize the resulting product with non-ridging characteristics upon being drawn, and the remainder iron and incidental impurities.

2. A non-ridging ferritic stainless steel having a composition consisting essentially, by weight, of about 14 to 25 percent of chromium, up to about 0.60 percent of carbon, up to about 1.25 percent of manganese, a

4 maximum of one percent of silicon, a small amount up to 0.7 percent of columbium elfective to characterize the resulting product with non-ridging characteristics upon being drawn, and the remainder iron and incidental impurities.

3.A non-ridging ferritic stainless steel consisting essentially of, by weight, 14 to 18 percent of chromium, 0.20 percent maximum of carbon, up to 1 percent of manganese, up to 1 percent of silicon, up to 0.04 percent of phosphorus, up to 0.03 percent of sulfur, about 0.1 to 0.7. percent of columbium and the remainder iron together with incidental impurities.

4. A non-ridging ferritic. stainless steel having a composition consisting essentially, by weight, of 14 to 18 percent of chromium, 0.20 percent maximum of carbon, up 'to one percent of manganese, up to one percent of silicon, up to 0.04 percent of phosphorus, up to 0.03 percent of sulfur, 0.30 to 0.60 percent of columbium and the remainder iron together with incidental impurities.

5. An alloy sheet having a composition of A.I.S.I. Type 430 to which has been added 0.40 to 0.50 Weight percent of columbium, said sheet being characterized by the absence of ridging upon being drawn.

6. A deep drawn article free from ridging and having a composition in accordance with claim 1.

7. A deep drawn article free from ridging and having a composition in accordance with claim 3.

References Cited in the file of this patent UNITED STATES PATENTS 1,954,344 Becket et al Apr. 10, 1934 2,046,012 Becket et a1 June 30, 1936 2,673,166 Carruthers Mar. 23, 1954 Kiefer et al. Dec. 4, 1956 OTHER REFERENCES 

1. A NON-RIDGING FERRITIC STAINLESS STEEL CONSISTING ESSENTIALLY, BY WEIGHT, OF ABOUT 14 TO 25 PERCENT OF CHROMIUM, UP TO ABOUT 0.60 PERCENT OF CARBON, UP TO ABOUNT 1.25 PERCENT OF MANGANESE, A MAXIMUM OF ONE PERCENT OF SILICON, A SMALL AMOUNT THAT IS LESS THAN ONE PERCENT OF COLUMBIUM EFFECTIVE TO CHARACTERIZE THE RESULTING PRODUCT WITH NON-RIDGING CHARACTERISTICS UPON BEING DRAWN, AND THE REMAINDER IRON AND INCIDENTAL IMPURITIES. 